Radiation-induced electrolytic phenomena with differential radiation cell in water-cooled nuclear reactors

•Confirmed the differential radiation cell causing radiation-induced electrolysis phenomena.•Potential differences are induced between in- and out- core regions due to radiation difference.•Dissolved species are reduced at the in-core and oxidized at out-core regions inducing voltages.•Between these two regions, the charge transfer occurs with conduction- and valence electrons.•Close circuit corrosion should be induced through radiation-induced electrolysis mechanism.

BackgroundThe “differential radiation cell (DRC)” is an adaptation of “differential aeration cell” which is widely applied in conventional corrosion studies. However this mode of corrosion has been dismissed in the nuclear community considering that the transport of ions with flow is unlikely due to the high purity of reactor water. The author found that the analogous mechanism should be occurring in reactor water with radiation differences. This phenomenon should be inducing a severe interaction between structural materials and their environments found in light water reactors through “radiation-induced electrolytic (RIE)” corrosion.ObjectiveThis review is to elucidate the RIE mechanism and confirm the existence of a DRC occurring by way of transporting valence electrons of dissolved hydrogen and oxygen. These species are reduced (capturing electrons) at the reactor core region behaving as a gigantic cathode and oxidized (losing electrons) back at the anodic out-of core region, resulting in a closed electrical circuit.Material and methodThe author will first introduces and reviews the published experimental evidence focusing on the observed potential differences between the in-core and out-of-core regions. Present a new theoretical model developed by integrating high temperature electrochemistry with the radiation chemistry material balance equation. Finally modeling studies are performed to theoretically reproduce the experimental results.ResultsElectrode kinetic effects in the out-of-core regions were found essential in maintaining the overall material balance of dissolved species. The experimental results were reasonably well reproduced by using the standard equilibrium potential as a fitting parameter, in effect considering it as a formal potential in describing the in-core chemistry.ConclusionThe reported in-pile test results as well as the modeling studies elucidated the DRC mechanism and confirmed the potential root cause of several RIE phenomena including the aggravation of corrosion in LWRs.

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